Dyeing Polymorphs:  The MALDI Host 2,5-Dihydroxybenzoic Acid

• Published in: Crystal growth & design Vol. 7; no. 3; pp. 492 - 495
• Main Authors: Cohen, Dawn E, Benedict, Jason B, Morlan, Brian, Chiu, Daniel T, Kahr, Bart
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 01.03.2007
• Subjects: Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Exact sciences and technology; Organic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Organic dye; Force field; Inspection; Mass spectroscopy; Desorption; Crystal field; Lattice parameters; Laser desorption; Benzoic acid derivatives; Ionization; Cocrystal; Polymorphism; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg060887w

The dye methyl red was used to distinguish concomitant polymorphs of the matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) host, 2,5-dihydroxybenzoic acid. Red and purple crystals were readily separated by inspection. They corresponded to the known Form I (P21/c, a = 4.9110(3) Å, b = 11.8280(7) Å, c = 11.0580(6) Å, β = 91.059(3)°, V = 642.22 Å3) and Form II (P21/c, a = 5.5610(2) Å, b = 4.8690(1) Å, c = 23.6880 (8) Å, β = 100.191(1)°, V = 631.27 Å3), respectively. X-ray structures of cocrystals of dihydroxybenzoic acids and methyl red, measurements of the linear dichroism of mixed crystals, and force-field calculations were used to investigate the mechanism of differential coloring. The relevance of the observations to investigations of the MALDI mechanism are discussed.